Generally, a recent trend is for control measuring instruments, such as a temperature controller, a signal converter, a panel meter, and the like, to receive various possible electrical signals using a simple input circuit so as to implement operation convenience of a user, extension of applications, and saving of manufacturing costs. FIGS. 1 to 3 show a configuration example of a multi input circuit according to the related art so as to simplify an input circuit.
First, one configuration example according to the related art shown in FIG. 1 consists of a temperature sensor signal input terminal and a current signal input terminal, respectively, wherein an RTD temperature sensor signal is received through a first terminal, a second terminal, and a third terminal and a TC temperature sensor signal or a voltage signal is received through the second terminal and the third terminal, but a current signal needs to be converted into the voltage signal and therefore, is received by a current signal detection resistor through the third terminal and a fourth terminal connected at both ends of the detection resistor.
However, the input circuit as described above is simple in terms of a configuration but requires a relatively large number of input terminals, such that manufacturing costs are increased and there is a limitation in miniaturization of products.
Another configuration example according to the related art of FIG. 2 relates to a method of passively connecting a current signal detection resistor using a separately provided input select switch 10 when an analog current signal is an input to convert and input the input current signal into voltage by the detection resistor, instead of commonly using a temperature sensor signal input terminal and an input terminal of an analog voltage signal or an analog current signal so as to minimize the number of input terminals, such that the input terminal and the configuration circuit may be simplified, but there may be inconvenience due to the use of the separate input select switch 10, the measuring error may occur due to the contact resistance of the input select switch 10, and the manufacturing costs may be increased.
Yet another configuration example according to the related art of FIG. 3 relates to a method for simplifying the input terminal and the configuration circuit and is similar to the method shown in FIG. 2, but is a method of allowing a user to separately wire a current signal detection resistor 20 for receiving the analog current signal instead of the input select switch 10 to an outside of a terminal, such that the input terminal and the configuration circuit may be simplified but the user inconvenience may be caused, there may be a difficulty in handling due to the equipping of current signal detection resistor 20, and it is impossible to implement the automation of the input selection.